<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>js变量来做算数</title>
</head>

<body>
    <p>假设 y=5，计算 x=y+2，并显示结果。</p>
    <button onclick="myFunction()">点击这里</button>
    <p id="demo"></p>
    <script>
        function myFunction() {
            var y = 5;
            var x = y + 2;
            var demoP = document.getElementById("demo");
            demoP.innerHTML = "x=" + x;
        }
    </script>
</body>

</html>